This invention relates to contacting devices, especially semiconductor devices during laser probing.
Semiconductor devices can be tested in various ways. One test technique involves probing a semiconductor device with light finished by a laser. During such testing, ohmic heating in the device causes its temperature to rise. Inasmuch as excessive heat can damage a semiconductor device, a heat sink is commonly provided for removing heat from the device. The heat sink can take various forms.
Referring to FIG. 1, U.S. Pat. No. 5,895,972 illustrates how an uncapped semiconductor device 10 provided with flip-chip packaging is conventionally probed with infrared (xe2x80x9cIRxe2x80x9d) light 12 provided from IR laser 14. Device 10 consists of semiconductor die 16, ball bonds 18, package 20, and pins 22 arranged as indicated in FIG. 1. Because device 10 is uncapped, only part of package 20 appears in FIG. 1. Incident IR light 12 strikes metallic part 24 of die 16. Portion 26 of incident light 12 is reflected off part 24 and detected by light detector 28.
During laser probing, heat is removed from semiconductor device die 16 by a heat sink consisting of thermally conductive IR-transparent pane 30 and heat spreader 32 that overlies and contacts one of the faces of die 16. Incident light 12 and reflected light 26 pass through pane 30 formed with IR-transparent material such as diamond. Heat spreader 32, typically consisting of copper or aluminum, is thermally connected to pane 30 generally along its outer lateral periphery. Heat produced in die 16 is transported through pane 30 to spreader 32 where the heat energy spreads out and dissipates.
IR-transparent panes, such as pane 30, are typically quite delicate, especially since they need to be relatively thin to transmit an adequate fraction of incident IR light. Such IR-transparent panes can readily be damaged when they are brought into contact with semiconductor devices that are to undergo testing, particularly laser probing. Accordingly, it would be desirable to have a technique for contacting a semiconductor device with a delicate IR-transparent pane in such a manner as to substantially reduce the likelihood of damaging the pane. It would also be desirable to improve the heat transfer from the semiconductor device through the pane to an adjacent heat spreader.
The present invention furnishes an apparatus and associated method for bringing a device, such as a semiconductor device, into contact with a light-transparent pane in a way that can be readily controlled to substantially avoid damaging the pane. Light provided, for example, by a laser for probing the device can be directed toward the pane from opposite the device so as to pass through the pane and impinge on the device.
More particularly, an apparatus in accordance with the invention contains a contacting component, a pane component, a heat spreader, and an attachment mechanism. The contacting component contacts the device. The pane component includes a light-transparent pane for contacting the device. The heat spreader contacts, or is connected to, the pane component.
The attachment mechanism attaches the heat spreader to the contacting component across an adjustable spacing between the heat spreader and the contacting component. The attachment mechanism also adjusts the adjustable spacing between the heat spreader and contacting component, and three-dimensionally restricts movement of the heat spreader relative to the contacting component across the adjustable spacing. With the pane component positioned close to the device, the attachment mechanism is adjusted to reduce the spacing between the heat spreader and the contacting component so as to cause the light-transparent pane to contact the device.
As the adjustable spacing is being adjusted, the attachment mechanism exerts a primary force on the heat spreader toward the contacting component across the adjustable spacing. This causes the device to exert a corresponding force on the pane. The attachment mechanism preferably employs one or more springs in such a manner that the force exerted by the attachment mechanism on the heat spreader varies across a relatively small range. As a result, the force exerted by the device on the pane is limited to some maximum value. By choosing the force exerted by the device on the pane to be sufficiently small as the spacing between the heat spreader and contacting component is adjusted to bring the pane into contact with the device, the pane does not undergo significant damage due to contacting the device.
The heat spreader is preferably implemented as a main spreader body formed with copper and an overlying surface layer formed with gold. This combination of metals improves the heat transfer from the pane to the spreader. When the heat spreader is connected through indium to a surface region of the pane component, the indium and the gold of the spreader surface layer typically achieve a good thermal connection to further improve the heat transfer.